1. Field of the Invention
This invention relates to organic polymer compositions. More particularly, this invention relates to film-forming polymer compositions containing from 0 xcexcp to about 50 weight percent of pigments and a specified class of esters of benzoic acid to improve certain properties of film-forming compositions and/or films prepared using these compositions. The film-forming polymer in the present compositions is prepared from at least one ethylenically unsaturated ester.
2. Description of the Prior Art
Esters derived from benzoic acid and alcohols containing from 2 to 20 or more carbon atoms are known as plasticizers for homopolymers and copolymers of vinyl chloride. For example, German published application (Offenlegungsschrift) No. 1,962,500 teaches using benzoic acid esters of the formula PhC(O)OR or succinic acid esters as plasticizers for polymers derived at least in part from vinyl chloride. In this formula Ph represents a phenyl radical and R represents an alkyl radical containing from 8 to 13 carbon atoms. The alcohol portion of the succinic acid esters contains from 8 to 13 carbon atoms.
Depending upon the desired end use application, the vinyl chloride polymer can be in the form of an aqueous emulsion that is used either alone or in combination with a powdered solid form of the polymer.
Another group of organic polymers that are useful in film-forming compositions are homopolymers and copolymers prepared from ethylenically unsaturated esters. The ethylenic unsaturation can be in the carboxylic acid or alcohol portion of the ester molecule. Suitable ethylenically unsaturated acids include but are not limited to acrylic and methacrylic acids. The alcohol portion of these esters typically contains from 1 to 4 or more carbon atoms. This family of polymers is referred to as xe2x80x9cacrylic polymersxe2x80x9d. These polymers can optionally include repeating units derived from ethylenically unsaturated hydrocarbons such as ethylene and styrene.
Vinyl acetate is an example of a polymerizable ester derived from an ethylenically unsaturated alcohol and a saturated carboxylic acid. Copolymers of vinyl acetate and olefins such as ethylene are useful for aqueous adhesive compositions.
U.S. Pat. No. 5,236,987 to William Arendt, which issued on Aug. 17, 1993, teaches using certain esters of benzoic acid as coalescents and plasticizing agents for water-based paint compositions containing an emulsified acrylic polymer as the film-forming material. The alcohol portion of the benzoic acid ester contains from 8 to 12 carbon atoms and the polymer is typically present in the composition as an aqueous emulsion.
The major ingredients of the paints described in the Arendt patent typically comprise an emulsified film-forming polymer derived from at least one ester of acrylic and/or methacrylic acid, water, a pigment, a thickening agent and at least one surfactant. The combination of pigment and thickening agent typically constitutes from 20 to 50 percent by weight of the total paint composition.
Film-forming compositions such as inks, adhesives and floor polishes contain different ingredients and types of film forming polymers than paints. Even though the polymers in these compositions are prepared from the same class of monomers as those present in paints, the type(s) of monomer(s), the molecular weight of the polymer, and the presence and interaction of the additional ingredients present in the various types of compositions make it difficult to predict how a coalescent, leveling agent and/or plasticizer suitable for use paint compositions will affect the properties of other film-forming compositions, such as adhesives and polish formulations, and the properties of the resultant films.
European Patent No. 668,338 issued to Rohm and Haas describes adhesive compositions wherein the film-forming material is an acrylic polymer. In addition to the polymer the compositions also include from 0.1 to 40 parts by weight per 100 parts of polymer of a plasticizer. Suitable plasticizers include benzoic acid esters derived from diethylene glycol and/or dipropylene glycol. No benzoate esters derived from aliphatic alcohols are disclosed.
U.S. Pat. No. 5,368,795, which issued on Nov. 29, 1994 to Quadir describes aqueous ceramic slurries containing an ethylene/vinyl acetate copolymer and a plasticizer. While esters of benzoic acid are disclosed as a class, the only specific ester mentioned is dipropylene glycol dibenzoate.
Published PCT Application No. 9,856,867 published on Dec. 17, 1998 describes an adhesive for polyvinyl chloride-based flooring materials. The adhesive contains an aqueous dispersion of an acrylic polymer and a plasticizer. To reduce the volatility of the composition the plasticizer is preferably diethylene glycol dibenzoate and/or dipropylene glycol dibenzoate.
Other classes of compounds disclosed as being effective coalescing, leveling, and/or plasticizing agents for compositions containing polymerized ethylenically unsaturated esters as the film-forming polymer include but are not limited to organic esters such as dioctyl adipate and 2,2,4-trimethyl-1,4-pentanediol mono- and diisobutyrates, esters of phthalic acid wherein the alcohol portion of the ester typically contains from 3 to 10 carbon atoms, partially etherified diols and triols such as 2-(2-ethoxyethoxy)ethanol, and trialkoxyalkyl phosphates such as tributoxyethyl phosphate. Some of these materials, particularly esters derived from aliphatic carboxylic acids such as adipic acid, do not substantially improve either the film-forming properties of aqueous polymer compositions typically used as adhesives, inks, floor polishes and unpigmented coatings, or the appearance of films formed from these compositions.
The present invention is based on the discovery that of the many known classes of coalescing, leveling and plasticizing agents, benzoic acid esters of monohydric alcohols containing 8 carbon atoms are unique with respect to their ability to improve the properties of many types of film-forming compositions, including adhesives, floor polishes and non-pigmented coatings. In many instances the properties of films formed from these compositions are also improved.
Because the various types of film-forming compositions differ considerably from one another with respect to composition and molecular weight of the film-forming polymer and the types of additional required and optional ingredients, one skilled in the art would consider it unlikely that one type of plasticizer would improve the properties of these substantially different compositions.
The present compositions comprise at least one acrylic, vinyl acetate or epoxide polymer or copolymer as the film-forming ingredient and, as a plasticizer, an ester of benzoic acid wherein the alcohol portion of the ester is alkyl and contains eight carbon atoms. In preferred compositions this alcohol portion is derived from 2-ethylhexyl.
Additionally, in some of the present compositions the benzoic acid ester has been found to interact synergistically with benzoic acid esters derived from oligomeric ethylene glycols.
The present invention provides a film-forming composition comprising:
A) a polymer selected from the group consisting of
(1) homopolymers and copolymers of esters of acrylic and methacrylic acids;
(2) said copolymers wherein a portion of the repeating units are derived from at least one acid selected from the group consisting of acrylic and methacrylic acids;
(3) copolymers of styrene and at least one member selected from the group consisting of esters of acrylic and methacrylic acids;
(4) said copolymers of styrene wherein a portion of the repeating units are derived from at least one acid selected from the group consisting of acrylic and methacrylic acids;
(5) homopolymers of vinyl acetate;
(6) copolymers of ethylene and vinyl acetate; and
(7) homopolymers and copolymers of organic compounds containing at least two epoxide groups per molecule
B) an amount sufficient to improve the properties of said films of at least one benzoic acid ester exhibiting the general formula PhCO(O)R1, where Ph represents a phenyl radical and R1 represents a linear or branched hydrocarbon radical containing 8 carbon atoms.
In addition to being more effective plasticizers relative to related benzoic acid esters such as isodecyl benzoate, the present esters sometimes interact synergistically with benzoic acid esters derived from oligomeric ethylene glycols. Examples of these glycol esters include but are not limited to diethylene- and triethylene glycol dibenzoates. As used in the present specification, synergistic interaction implies that the level of certain properties exhibited by a composition containing this combination of benzoic acid esters and/or the films prepared using these compositions are superior relative to the property levels predicted based on the levels imparted by the individual esters used at the same concentration as the blend.
In preferred synergistic combinations, some property levels imparted by the present alkyl benzoates are typically lower than the properties observed using a more expensive plasticizer such as di- or triethylene glycol benzoates and mixtures thereof. The unexpected ability of the present alkyl benzoates, specifically 2-ethylhexyl benzoate, to replace 50 weight percent or more of the considerably more expensive glycol-based benzoate without sacrificing desirable properties such as rapid viscosity development of an adhesive and leveling of a liquid film provides a considerable and unexpected economic advantage for the compositions of the present invention containing this combination of benzoic acid esters.
Some of the specific classes of film-forming compositions suitable for use with the benzoic acid esters and synergistic benzoic acid ester blends of the present invention together with the property improvements imparted by these esters will now be described in detail.
Floor Polishes
A preferred end-use application of the present alkyl benzoates is as a leveling aid for polish compositions intended for use on linoleum and other types of flooring materials containing a wear layer formed from a homopolymer or copolymer of vinyl chloride.
Prior art floor polishes typically contain the following ingredients
1) an aqueous emulsion of a) a homopolymer or copolymer derived from at least one ester of acrylic or methacrylic acid wherein the alcohol portion of the ester contains from 1 to 8 carbon atoms or 2) a copolymer derived from at least one of these esters and up to 20 weight percent, based on total repeating units in said polymer, of styrene;
2) a glycol ether such as diethylene glycol monomethyl ether as a coalescing agent;
3) a solubilized resin such as a rosin-based resin;
4) an aqueous emulsion of an organic wax such as a polyethylene wax; and
5) from 2 to about 4 weight percent of a leveling aid that is typically an ester of phosphoric acid such as tributoxyethyl phosphate.
In addition to the aforementioned ester monomers, the film-forming polymer may also contain a small concentration, typically less than about 5 weight percent, of units derived from acrylic and or methacrylic acid as a solubizing aid. Relatively minor amounts of additional ingredients such as defoamers, wetting agents, biocides and auxiliary plasticizers can also be present. Isodecyl benzoate is an example of a auxiliary plasticizer typically used in polish compositions for floors.
The present inventors discovered that one of the present benzoic acid esters derived from a monohydric alcohol containing eight carbon atoms can replace three of the ingredients typically present in floor polish compositions, namely 1) the phosphate esters conventionally used as the leveling agent; 2) the aromatic and aliphatic acid esters such as isodecyl benzoate typically used as auxiliary plasticizers; and 3) the esters typically used as coalescing agents. The film formed when the resultant formulation is applied to the polyvinyl chloride wear layer of a flooring material exhibits leveling and an appearance comparable to the phosphate-containing control.
The properties imparted by one of the presently preferred benzoic acid esters, 2-ethylhexyl benzoate, are further improved when the ester is used in synergistic combination with diethylene glycol dibenzoate and/or triethylene glycol dibenzoate. Preferably both of the glycol esters are present in a weight ratio of 1 to 3 parts of the diethylene glycol dibenzoate to 1 part of the triethylene glycol ester.
Films formed when compositions containing these combinations of esters are applied to the polyvinyl chloride wear layer of a flooring material exhibit film leveling and gloss equivalent to prior art phosphate-containing compositions. These properties are typically superior to those achieved using one or both of the constituent benzoic acid esters types (alkyl and glycol) alone at the same concentration as the combined esters.
Adhesives
A second type of film-forming composition exhibiting improved properties and/or processability using the present class of benzoic acid esters are adhesives containing as the film-forming polymer a vinyl acetate homopolymer or a copolymer of vinyl acetate and ethylene containing from 3 to about 10 weight percent of repeating units derived from ethylene. The polymer is present as an aqueous emulsion. Techniques for the emulsion polymerization of ethylenically unsaturated monomers are well known.
In addition to the emulsified film-forming polymer, which can constitute up to 95 weight percent of the adhesive, typically from 30 to about 70 weight percent, and from 5 to about 25 weight percent of a plasticizer, the adhesive compositions typically contain a thickening agent such as cellulose, a water-miscible organic solvent such as a polyhydric alcohol, from 0 up to about 15 weight percent of a filler and up to 5 weight percent of a humectant such as glycerin or propylene glycol.
Benzoic acid esters derived from oligomeric glycols such as diethylene glycol and dipropylene glycol are typically used as plasticizers in aqueous adhesive compositions because these esters are solids at room temperature (typically 25xc2x0 C.), and therefore do not significantly increase the volatile organic content (V.O.C.) of the composition. In many countries V.O.C. levels are strictly controlled by government regulations.
The prior art teaches that benzoates derived from glycols such as diethylene glycol, triethylene glycol and dipropylene glycol are very desirable for use in adhesives because they provide the desired viscosity increase, open time and set time.
xe2x80x9cOpen timexe2x80x9d refers to the period of time during which a satisfactory bond can be formed between adhesive and the substrate. xe2x80x9cSet timexe2x80x9d is defined as the time period required for cohesive failure to occur at the bonding surfaces of two substrates bonded by the adhesive.
The major disadvantage of benzoic acid esters derived from oligomeric glycols is their cost.
The primary function of plasticizers in adhesives is to increase the viscosity of the composition. The efficiency of a plasticizer is based on the viscosity increase achieved per unit weight of plasticizer. The present benzoic acid esters, particularly 2-ethylhexyl benzoate, are unexpectedly more efficient than a related alkyl benzoate derived from isodecyl benzoate. The unexpectedly high efficiency of 2-ethylhexyl benzoate makes it possible to replace up to 60 weight percent of one or more glycol dibenzoates with this alkyl benzoate. This preferred combination achieves the same increase in viscosity and values of set and open times with a relatively small increase in V.O.C., and is suitable for use in many end-use applications where V.O.C. levels approaching 0 are not an overriding consideration.
Inks
Water-based flexographic inks used in the printing industry are typically emulsions containing 1) at least one emulsified copolymer derived from acrylic and/or methacylic acid esters; 2) at least one emulsified organic wax; at least one alcohol containing from 2 to 4 carbon atoms, ammonia, water and about 4 weight percent of a coalescent that is typically a partially etherified glycol such as diethylene glycol. The organic polymers and wax typically constitute from 50 to about 60 weight percent of the composition and the pigment from 15 to about 20 weight percent.
The benzoic acid esters of the present invention can replace the partially etherified glycols typically used as coalescing agents for this type of ink composition, but may offer additional advantages as plasticizers and/or viscosity modifiers.
Epoxy Coatings Formulations
The plasiticizer compositions of the present invention can be used to improve the film-forming properties of aqueous compositions containing as the film-forming polymer an organic compound containing at least two epoxide groups per molecule. The hydrocarbon radical in which the epoxide groups are present can be aliphatic, cycloaliphatic or aromatic.
Examples of epoxy coating formulations suitable for use with the plasticizers of the present invention include aliphatic diepoxides such as 1,2,9,10 decanediepoxide, cycloaliphatic diepoxides such as 1,4-cyclohexane diepoxide and aromatic diepoxides such as the diglycidyl ethers of the various bis-phenols, including bis-phenol A crosslinked with aliphatic, cycloaliphatic or aromatic amines.
Benzyl alcohol and related alcohols have been used as plasticizers in epoxy coating formulations. The use of benzoic acid esters of the present invention as replacements for all or part of these alcohols allows the coatings formulator to produce low volatile organic content coatings while retaining the viscosity and solvating characteristics of the alcohols.
In addition to the aforementioned applications the benzoic acid esters of the present invention can be used in latex caulk formulations in place of the aliphatic acid esters currently used to improve the paintablilty of the composition following application and curing.
The following examples demonstrate the desirable properties imparted to different types of film-forming compositions by the benzoic esters of the present compositions. These examples should not be interpreted as limitations on the scope of the present invention as defined in the accompanying claims.